ECC (either "error correction [or correcting] code" or "error checking and correcting") allows data that is being read or transmitted to be checked for errors and, when necessary, corrected on the fly.

The above error indicates the l3 cache that the cpu is using has detected an unrecoverable error...Since your using an opteron cpu and they have integrated l3 cache on the cpu, you most likely have a bad cpu. I would pull the heatsink/verify it is seated correctly and or reseat. If you continue to have issues I would rma.